It is important in various processes to diffuse a gas into a body of liquid in a manner that will disperse the gas uniformly through a large portion of the liquid and result in as rapid as possible absorption of the gas by the liquid. Diffusion of a gas into a body of liquid in this way is useful, for example, in a large number of chemical and petrochemical processes. It is also important in certain sewage treatment processes. It is becoming increasingly important in the treatment of natural bodies of water with air, oxygen, or ozone in order to revive polluted rivers, lakes, bays, etc.
When, for purposes of economy or for any other reason, gases used in the treatment of a body of liquid should not be allowed to escape from the surface of the liquid, it is important that the method and apparatus used be such that all, or nearly all, the gas dissolves in the liquid before any substantial number of gas bubbles can rise to the surface. In every case, it is usually desirable that the absorption of the gas into the liquid proceed as rapidly as possible.
It has long been known that method and apparatus employing the phenomenon known as "bubble shearing" are well adapted to the production of quite small gas bubbles in a liquid. In this method, a gas is passed through the capillary passages of a foraminous material to be introduced into a stream of liquid on the other side of the material. The gas emerges at the boundary surface or gas diffusing surface of the foraminous material in a number of locations spaced from each other, where it starts to form a plurality of fine bubbles, or in other words forms "nascent" gas bubbles. The liquid into which the gas is thus introduced is caused to move more or less rapidly past the capillary openings of the foraminous material. As a result, the viscous shear forces exerted by the moving body of liquid shear off the partially formed or nascent gas bubbles before they can grow to such a size that their natural buoyancy in the liquid will cause them to break the surface tension that tends to hold them on the boundary surfaces of the gas transmitting foraminous material.